1. Field of the Invention
The present invention relates to an automobile engine control system which establishes the amount of fuel injection based on a predicted amount of intake air and sets the timing of ignition based on the actual amount of intake air.
2. Description of Related Art
In recent years, electronically controlled engines have been widely used, which control the air-fuel ratio of a fuel mixture and the timing of ignition in accordance with driving conditions so as to improve its emission control characteristics or fuel consumption efficiency. With such an electronically controlled engine, a fuel injection valve, which injects a fuel into an air intake line, is controlled by a control unit comprising a microcomputer to set the amount of fuel injection so that the air-fuel ratio of the vaporized fuel mixture in the combustion chamber matches a specific target ratio for each combustion cycle. In other words, the control unit computes the ratio of intake air charged into the combustion chamber (air charging efficiency) for each combustion cycle so as to cause the fuel injector to inject fuel with a specific ratio relative to the air charging efficiency. The amount of air charged into the combustion chamber for each combustion cycle is basically computed by the control unit based on the amount of intake air detected by an air flow sensor and the rotational speed of engine detected by a speed sensor. Also, the timing of ignition is appropriately established by the control unit according to the amount of charged air.
In the ordinary fuel injection type of engines, in order to promote the mixing of fuel and intake air through contact between the two for a period of time as long as possible, the injection of fuel from the fuel injection valve is accomplished during the first half of an air intake stroke. Accordingly, it is essentially required to determine the amount of air to be charged into the combustion chamber prior to the commencement of fuel injection, i.e. at the beginning of the air intake stroke, for each combustion cycle. For this requirement, conventional electronically controlled engines typically compute the amount of intake air to be charged into the combustion chamber for each combustion cycle based on the amount of intake air detected at the beginning of an air intake stroke. However, when the charging amount of intake air for each combustion cycle is computed based on the amount of intake air at the beginning of the air intake stroke, the charging amount of air for each combustion cycle is not correctly detected during non-steady driving, such as during acceleration or deceleration. This is because there occurs changes in the amount of air introduced into the intake line with time during acceleration or deceleration and, consequently, it is difficult to detect the accurate amount of intake air. This leads to a deviation of the air-fuel ratio of a fuel mixture from the target ratio, resulting in deterioration in fuel consumption efficiency or in emission control characteristics.
In improved electronically controlled engines, the amount of intake air at the end of an air intake stroke is predicted or estimated based on the amount of intake air at the beginning of the air intake stroke and the rate of change in the amount of intake air at the same time. Then, on the basis of the predicted amount of intake air, the charging amount of intake air is computed for each combustion cycle, upon the basis of which the amount of fuel injection and the timing of ignition are determined. Such an electronically controlled engine is known from, for instance, Japanese Unexamined Patent Publication No. 63-8296.
However, in the electronically controlled engine described in the above publication, in which the amount of intake air is predicted or estimated at the end of an air intake stroke and the charging amount of air charged into the combustion chamber for each combustion cycle is computed based on this predicted amount of intake air, even though the predicted charging amount of intake air is ideal or optimum as a parameter for setting of the amount of fuel injection, it is not necessarily appropriate or optimum as a parameter for setting of the timing of ignition. As a result, with the electronically controlled engine, the timing of ignition, or the angle of advancement, deviates from the optimal timing, creating the problem that fuel consumption efficiency or emissions control characteristics can not be sufficiently enhanced.